I would certinly defer to wanabeflyers excellent post with one small caveat. im a bit unclear on how much us/foriegn travel you do. If the majority is in the usa and upgrades are your primary goal then i agree that ua or aa are your best bet. If the majority of of your travel is to asia and other overseas destinations then you might want to consider the asiamiles/oneworld program, the partners include aa, cx, ba, jal and others because on the whole in my opinion they are just better than any american airline.